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Chemical Processes and Regional Modeling (CPRM) Group
CPRM Group Members:
Summary of Activities:MIRAGE
ACD scientists led a large community field campaign to examine the outflow of polluted air from Mexico City . The campaign involved about 400 investigators from US and Mexican universities and government agencies, as well as participants from other nations. The field campaign took place during 1-30 March 2006, with extensive ground-based measurements in and near Mexico City , five aircraft based in Veracruz and one aircraft based in Houston , coordinated satellite observations, and numerical modeling. The overall field campaign, called Megacity Initiative: Local and Global Research Observations (MILAGRO), consisted of four coordinated field campaigns: MCMA-2006 (México City Metropolitan Area - 2006) to examine emissions and boundary layer concentrations within México City . MAX-Mex (Megacity Aerosol Experiment in México City ) to examine the properties and evolution of aerosols and gas-aerosol interactions in the immediate urban outflow. MIRAGE (Megacity Impacts on Regional and Global Environments), to examine the evolution of the México City plume on larger regional scales. INTEX-B (Intercontinental Chemical Transport Experiment – Phase B), to study the evolution and transport of pollution on global scales. Sasha Madronich was the PI for MIRAGE and one of the four coordinators of MILAGRO.
The MILAGRO observations comprise a very large data set of gas phase concentrations, aerosol chemical, microphysical, and optical properties, radiation measurements, and supporting meteorological observation. Analysis of MILAGRO measurements is currently under way. Preliminary results show that the regional air quality is governed by a number of sources including urban pollution, dust, fires, and biogenic emissions, so that it should be possible to examine the behavior of pollutants under a variety of conditions.
ACD experimentalists participated in the intensive mission by making state-of-the-art measurements on board the NSF/NCAR C-130 aircraft and several ground sites near Mexico City . ACD modelers used global and regional models (MOZART and WRF-Chem) to generate numerical forecasts that were used in daily flight planning and are now used for more detail comparison with the measurements.
WRF-Chem
ACD scientists continued the development and application of the Weather Research Forecasting (WRF) model with on-line chemistry (WRF-Chem). The WRF-Chem model is being developed collaboratively with Georg Grell (NOAA) and Jerome Fast (DOE/PNNL). Xuexi Tie has implemented in WRF-Chem the fast photolysis scheme FTUV, improved emissions over Mexico , and improved boundary conditions derived from a global model.
Scientific studies were focused primarily on the Mexico City region, to support the MIRAGE field campaign and the interpretation of the measurements. The ability of the model to simulate the observed concentrations of urban pollution was demonstrated for Mexico City using available measurements for an earlier time period (May 2003). [ Tie, X, S. Madronich , GH. Li, ZM Ying, R. Zhang, A. Garcia , J. Lee-Taylor and Y Liu, Characterizations of Chemical Oxidants in Mexico City : A Regional Chemical/dynamical Model (WRF-Chem) Study, submitted to Atmos. Environ ., 2006.]
During the actual field campaign (March 2006), WRF-Chem forecasts were used extensively by ACD scientists during the MIRAGE field campaign, to assist in the planning of daily flight operations. Early comparisons with preliminary data suggest that the model does a reasonable job in prediction the location and chemistry of the Mexico City plume, but some differences are also seen that will require closer scrutiny.
Additional scientific studies with the WRF-Chem model looked at the chemical characterizations of soluble aerosols in the southern China region, and at the extent of biogenic VOC and NOx emission in the region of China [Tie, X., G. Li, Z. Ying, A. Guenther, and S. Madronich, Biogenic emissions of VOCs and NO in China and Comparison to Anthropogenic Emissions, in press, Science of Total Environ ., 2006; Wu, D., and X. Tie, Physical and Chemical Characterizations of Soluble Aerosols in Southern China, Chemosphere, 64, 749-757, 2006.]
Atmospheric UV Studies
The Tropospheric Ultraviolet VISIBLE (TUV) model was made available to the community through the NCAR/SCD Community Data Portal. Although it may be premature to give robust statistics, TUV downloads from (non-NCAR) community users continue at a rate of about 2-4 per week.
Madronich, in collaboration with U. of Cordoba ( Argentina ) researchers Rafael Fernández , Gerardo Palancar, and Beatriz Toselli, added to TUV a fully explicit line-by-line calculation of the O2 Schumann-Runge bands (SRB) transmission. This explicit calculation allows testing of parameterization methods currently used in models, and also allows more accurate calculation of scattered radiation in the stratosphere and mesosphere. [Fernández, R. P., G. G. Palancar, S. Madronich, and B. M. Toselli, Photolysis rate coefficients in the upper atmosphere: Effect of line by line calculations of the O 2 absorption cross section in the Schumann-Runge bands, accepted, J. Quant. Spectroscopy Radiat. Transf ., 2006.]
Madronich, together with medical researchers J. Cannell (Atascadero State Hospital), R. Wieth (Mount Sinai Hospital, Toronto), J. Umhau (NIH), M Holick (Boston U.) W. Grant (SUNARC), C. Garland (U. California San Diego) and E. Giovannucci ( Harvard U. ) examined the causes for the seasonal dependence of influenza epidemics. Based on a critical review of the literature, they hypothesize that the low wintertime UV levels at temperate latitudes lead to common vitamin D deficiency which in turn may be associated with higher risks of influenza epidemics. [Cannell, J., R. Vieth, J. Umhau, M. Holick, W. Grant, S. Madronich, C. Garland, and E. Giovannucci, Epidemic influenza and vitamin D, accepted, Epidemiology and Infection , 2006.]
NCAR Master Mechanism
Julia Lee-Taylor and Madronich continued the development of the Self-Generating Master Mechanism, the only fully explicit mechanisms for the gas-phase atmospheric oxidation of hydrocarbons. An important recent addition is a set of subroutines to formulate the chemistry of cyclic alkanes and alkenes. Preliminary simulations of the Mexico City atmosphere suggest that the gas phase chemistry produces multifunctional intermediates in an amount comparable to the observed organic aerosol loading, adding validity to the hypothesis that most of the organic aerosol is formed by gas-aerosol conversion in the atmosphere (secondary production) rather that direct emission.
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